Note : The negative clipping with basic parallel clipper can be achieved by reversing the direction of diode.

When Vin is positive then the diode is reversed biased and acts as an open circuit. Thus the output voltage Vo is same as Vin for R1< < RL. Hence the positive half cycle of Vin gets reproduced at the output. This is shown in the Fig. 1.

Fig. 1 Basic parallel clipper

Fig. 2 Basic parallel clipper ( Negative clipping)

The magnitude of the output voltage is,

Consider the negative half cycle of Vin. As Vin decreases below zero and becomes -0.7 V, the diode becomes forward biased and acts conducting. As long as Vin< -0.7 V, the diode remains ON and drop across it is cut-in voltage Vγ= 0.7 V, with polarities as shown in the Fig. 2(a).

Note : As diode and RL are in parallel, the output voltage is equal to the drop across diode i.e. 0.7 V in opposite direction.

The overall input-output waveforms can be shown as in the Fig. 3. The
Fig.4(a) shows the waveforms with piecewise model of diode while the
Fig. 4(b) shows the waveforms with an ideal diode approximation with Vγ = 0 V.